> moduli generated by OpenSSL will always have the high bit set

Correct for 1024, but...

    openssl genrsa 1023 | openssl rsa -text -noout

Also just noticed that openssl rsa actually has a -modulus switch so you can make do with "cut -b9-"

Ah, yeah, should have clarified that for any 8n-bit moduli it will be set.